The present invention relates to the field of photography and, more specifically, to self-processing or self-developing film units.
For over thirty years now, commercially available self-developing film units have included a rupturable pod or container holding a supply of a relatively high viscosity (compared to water) liquid processing composition. The pod is attached to a leading end portion of a sheet-like film component which includes one or more photosensitive layers and an image receiving layer. Following exposure in a self-developing camera, the film unit is advanced, pod first, between a pair of camera mounted compressive pressure applying rollers. Initial compression of the pod generates hydrostatic pressure in the liquid which is effective to rupture a rear pod seal and discharge the liquid in a pool between a predetermined pair of layers at the leading end of the sheet-like film component. As the film unit is further advanced between the rollers, the compressive force thereon causes the liquid to be spread in a thin, substantially uniform, layer between the predetermined film layers to imbibe the photosensitive layer (or layers) and initiate a well-known development and diffusion transfer process that results in the production of a positive image in the image receiving layer.
Those skilled in the art of processing self-developing film units in this manner will appreciate that the quality of the positive image is critically dependent upon successfully spreading the viscous liquid, which has a jelly-like consistency, to provide a thin layer of processing composition having a substantially uniform thickness over the entire image forming area of the film component.
The seemingly simple task of spreading a thin, uniform layer of viscous liquid between two opposed layers of the film component is, in fact, quite difficult because of the numerous variables in the process. These variables include the specific viscosity and flow characteristics of the liquid, the resistance to flow characteristics of the opposed layers of the film component which depend upon the surface tension parameters of the layers and the spacing therebetween, the amount and lateral distribution of pressure applied by the rollers, and the rate of film advancement therebetween.
Contemporary self-developing photographic systems, such as the SX-70, One-Step and Sun Camera Systems manufactured and marketed by Polaroid Corporation, Cambridge, Mass. employ so-called integral or non-peel-apart film units and compact cameras having motorized roller drive systems. In these photographic systems the spread control function is divided between structures in the film unit, the cassette holding a stack of such film units, the pressure applying rollers, and a film deflector on the exit side of the rollers.
Components of the film unit which influence spreading characteristics include the structural configuration of the pod and its rear seal rupture characteristics, along with internal masks or side rails within the film component that the rollers ride along to control thickness of the liquid layer. The cassette is formed with a precision tapered wall section near the film exit slot which bears on an upper surface of the film unit as it is advanced into the rollers to control the shape of the pool of liquid discharged from the pod. The rollers are manufactured to extremely high tolerances and at least one of them may include an assymetrical shape, e.g. non-cylindrical tapered sections and red bar grooves of different configurations at opposite ends of the roller. The rollers are mounted in a precision spring biased bearing block assembly which controls the roller gap and the amount of compressive force applied by the rollers. The film deflector on the exit side of the rollers is precisely located with respect to the roller bite line or gap to induce a controlled large radius curve in the exiting portion of the film unit which further influences the liquid spreading in a beneficial manner.
While the above noted film, cassette, and camera structures and components provide excellent control over the liquid spreading function, they do add significant cost to the system because of the extremely tight tolerances to which these components must be manufactured and assembled.
Recognition of the undesirable high cost of precisely spreading a relatively high viscosity liquid processing composition has led to many proposed alternative systems that are well-known in the prior art.
Some of these alternative systems contemplate treating or wetting one outer surface of the exposed film component with a low viscosity (similar to water) liquid processing composition and employ a wide variety of structures and mechanisms to deliver the liquid to the surface that is to be wetted. The low viscosity liquid tends to be self-spreading and is much easier to disperse in a uniform manner than is the high viscosity liquid thereby dispensing with the need for elaborate and costly spread control components.
Other alternative self-developing film systems approach the problem by providing a pre-distributed layer of highly viscous or micro-encapsulated liquid processing composition on a separate processing sheet or web incorporated into the film component along with the photosensitive layers.
For representative examples of the latter approach, see commonly assigned U.S. Pat. No. 2,558,857 which discloses an elongated liquid and air impervious processing web coated with a jelly-like processing composition, and commonly assigned U.S. Pat. Nos. 2,543,181 and 3,306,747 wherein the processing liquid is pre-distributed within the film unit in a layer of micro-capsules or other frangible micro-containers, or is provided in a liquid impermeated layer of porous absorbent materials such as blotter paper.
Representative examples of self-developing film systems wherein the outer surface of an exposed photosensitive sheet is intended to be wetted with a low viscosity processing liquid may be found in U.S. Pat. No. 3,179,517 and commonly assigned U.S. Pat. Nos. 3,314,792; 3,345,165 and 3,907,563 wherein a processing web roll that is pre-soaked with a low viscosity liquid or is wetted just prior to processing is brought into face to face contact with an exposed photosensitive sheet to wet its outer surface and initiate the development process. Also, see commonly assigned U.S. Pat. Nos. 3,069,266 and 3,498,203 for examples of structures wherein a low viscosity processing liquid is delivered to the exposed film surface by means of various capillary action applicators.
U.S. Pat. No. 4,310,620 discloses a method of processing a photographic material by establishing contact between an outer surface of the material and a variety of flat, porous, capillary action spreading element impregnated with a low viscosity processing liquid. The spreading elements are porous structures in the form of individual sheets which may be woven or knitted fabrics, or non-woven webs of paper, or porous plastic or metal layers, or sponge or foam-like material, or hydrophillic material if an aqueous processing liquid is used. The spreading sheets may be presoaked with sufficient liquid to process a single film unit or may be provided in combination with a container of liquid that serves as a reservoir for providing additional liquid when the required volume of liquid for complete processing exceeds the liquid holding capacity of the spreading sheet. In one embodiment, the liquid impregnated sheet is initially provided in a water impervious container formed by laminating a water impervious foil on both sides of the impregnated spreader sheet. Before use the foil is stripped from one side to expose the impregnated spreading sheet which is then brought into contact with the surface of the exposed photographic material. In another embodiment, a rupturable container holding the processing solution is placed along one end of the spreading sheet. With this type of structure, the spreading sheet is placed on the photographic material surface and the two elements are advanced between pressure applying rollers which rupture the container and discharge the liquid so it is absorbed by the spreading sheet and transferred by capillary force to the outer surface of the photographic material. After processing, the spreading sheet may be stripped away or may be left in place.
As noted earlier, the cost of self-developing film units and cameras for exposing and processing these film units may be reduced substantially by switching from a high viscosity, jelly-like, liquid processing composition, to an easier spreading low viscosity processing liquid having a viscosity similar to water to eliminate the costs associated with providing precision film and camera components for accurately controlling the spread of high viscosity processing compositions.
The prior art self-developing film systems that employ a low viscosity processing liquid, noted above, have several drawbacks that severely limit their potential for commercial viability. For example, those systems that utilize a web roll of film component and a processing web roll that is to be wetted with the liquid and brought into face-to-face contact with the exposed film component require relatively large and awkwardly shaped camera housings to accommodate the web holding spools. Also, a cutting device is required for severing the individual frames after processing. Perhaps a more serious limitation is the need to provide complex liquid holding tanks or containers and seals for the exit slots thereof to prevent evaporation of the liquid and/or environmental contamination or degradation. Also, if the liquid is to be delivered intermittently to process successive film frames there is a tendency for porous or capillary applicators to clog as a result of dried fluid that crusts over the applicator tip.
While the porous capillary action spreading elements and liquid reservoir containers associated therewith described in the previously noted U.S. Pat. No. 4,310,620 apparently are designed for use with individual sheet components, as well as web roll film, the enumerated embodiments do not seem to be particularly practical for easy and reliable use and manipulation. For example, to use the embodiment wherein a pre-soaked pad or spreading element is enclosed in a water impervious container formed by foil sheets laminated on opposite sides of the spreading element, first one of the outer sheets must be stripped away to expose the surface of the spreading element which then must be registered over and placed in contact with the film surface to be wetted. Also, this means some provision must be made for conveniently disposing of the foil layer that is stripped away. In another embodiment, wherein the liquid is held in a rupturable pod at one end of the spreader element the applicator assembly must be moved into registration with the film element before the two are advanced between the pressure rollers. If the spreading element is predisposed over the surface to be wet during manufacture, that film surface is eliminated as an exposure surface thereby imposing a limitation on variety of film structures that may use this type of applicator.
Therefore, it is a primary object of the present invention to provide a low-cost, self-developing film unit that utilizes a low viscosity liquid processing composition and is easy and convenient to use. It is yet another object of the invention to provide such a film unit comprising a sheet like film component including an outer surface having a given predetermined area thereof that is to be wetted with such a low viscosity processing liquid to initiate processing, and a liquid applicator attached to the film component holding a supply of liquid sufficient to wet the given area.
It is yet another object of the invention to provide such a film unit wherein the applicator is preregistered with respect to the given area of the film component during manufacture.
Another object of the invention is to provide such a film unit wherein a component of the applicator initially serves to form a liquid and air impervious enclosure about the supply of processing liquid and is configured to be easily manipulated, following exposure, to present the liquid in face-to-face contact with a given area to effect wetting thereof.
Yet another object of the invention is to provide such a film unit that is configured to be compatible with a processing mechanisms for liberating the liquid from its applicator enclosure and delivering it to said given area.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.